Bypass for a hydraulic device

ABSTRACT

A bypass mechanism is provided for use in a hydrostatic transmission, to enable the user to open or close a valve between the two pressure sides of the hydraulic circuit of the transmission. An electrical mechanism is positioned to open or close the valve based on a signal which may be generated by a switch associated with the hydrostatic transmission.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/465,041 filed Jun. 19, 2003 now U.S. Pat. No. 6,735,943, which is acontinuation of U.S. application Ser. No. 10/036,835 filed Dec. 21, 2001now U.S. Pat. No. 6,588,206, which is a continuation of U.S. applicationSer. No. 09/627,569 flied Jul. 28, 2000, now U.S. Pat. No. 6,332,317,which is a continuation of U.S. application Ser. No. 09/223,673 filedDec. 30, 1998, now U.S. Pat. No. 6,145,312, all of which areincorporated herein by reference.

BACKGROUND

This invention relates to a electromechanical bypass for use in ahydrostatic transmission (“HST”). Hydrostatic transmissions are wellknown in the art, and are more fully described in, e.g., U.S. Pat. No.5,314,387, which is incorporated by reference herein. This invention canalso be adapted for use in an integrated hydrostatic transmission(“IHT”) incorporating gearing and axles within a single housing.

In general, an HST has a hydraulic pump and a hydraulic motor mounted ina housing. The pump and motor are hydraulically linked through agenerally closed circuit, and both consist of a rotatable body withpistons mounted therein. Hydraulic fluid such as oil is maintained inthe closed circuit, and the HST generally has a sump or reservoir fromwhich the closed circuit can draw oil from or dump oil to. This sump maybe formed by the housing itself.

The pump is usually driven by an external motive source such as pulleysor belts connected to an internal combustion engine. The pump pistonsengage a moveable swash plate and, as the pump is rotated by an inputsource driven by the external engine, the pistons engage the swashplate. Other HST designs may use a radial piston or ball piston pump andmotor design, but the general operation is similar. Movement of the pumppistons creates movement of the hydraulic fluid from the pump to themotor, causing rotation thereof. The motor pistons are engaged against afixed plate, and rotation of the motor drives an output shaft engagedthereto. This output shaft may be linked to mechanical gearing and axlesto drive a vehicle, which may be internal to the HST housing, as in anIHT, or external.

The pump/motor system is fully reversible in a standard HST. As theswash plate against which the pump pistons move is moved, the rotationaldirection of the motor can be changed. In addition, there is a “neutral”position where rotation of the pump does not create any movement of thehydraulic fluid. However, in most designs this neutral band is verynarrow, as it is dictated by the mechanical design of the unit and theuser's ability to mechanically locate the neutral area through use of ashift lever or foot pedal system.

The HST closed circuit has two sides, namely a high pressure side inwhich oil is being pumped from the pump to the motor, and a lowpressure, or vacuum, side, in which oil is being returned from the motorto the pump. When the pump direction is reversed, the two sides reverse,with the high pressure side becoming the vacuum side and vice versa.This circuit can be formed as porting formed within the HST housing, orinternal to a center section on which the pump and motor are rotatablymounted, or in other ways known in the art. Check valves are often usedto draw hydraulic fluid into the low pressure side to make up for fluidlost due to leakage, for example. Such check valves may be locateddirectly in the porting or maybe located in a center section andconnected to the closed circuit.

There is a need to have a means to open, or bypass, this closed circuitin certain circumstances. For example, when the vehicle is stopped, theoil in the closed circuit provides hydraulic braking, making itimpossible to manually move the vehicle. Mechanical bypass designs areknown in the art and are described in, for example, U.S. Pat. No.5,010,733. Such designs generally achieve bypass by opening the closedhydraulic circuit to the sump by, e.g., opening check valves in thecircuit, or by opening a shunt between the high pressure and lowpressure sides of the circuit.

However, such prior art designs have drawbacks. For example, in additionto those identified above, a completely open hydraulic circuit can leadto uncontrolled free-wheeling of the vehicle and create significantsafety risks. In addition, mechanical bypass mechanisms require variouslinkages from the HST and IHT to the vehicle, and it can be difficultfor the manufacturer of the HST or IHT to accommodate more than onestyle of actuation of the mechanical bypass.

SUMMARY OF THE INVENTION

This invention addresses the shortcomings in prior HST bypass designs.It is an object of this invention to provide an electromechanical bypasssystem for a hydrostatic transmission. This invention uses a simpleelectrical switch which may be triggered in various manners, and a meansfor creating a bypass condition in response to a first signal from saidswitch and closing the system in response to a second signal. Thisbypass may be achieved in a number of different ways, and the switchingmechanism could also be of a variety of forms.

It is a further object of this invention to provide an improved HSTdesign which gives the user a wider neutral band, through use of such aswitch in connection with the control mechanism of the vehicle to allowthe user to put the unit in bypass when the control mechanism is movedto the neutral position. Such a feature may be used in conjunction withor independent of another separate bypass switch.

It is yet another object to provide an improved bypass mechanism whichprevents uncontrolled free-wheeling of the vehicle. Additional objectsof this invention will be apparent upon review of the detaileddescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a tractor incorporating prior art mechanicalbypass mechanism.

FIG. 2 is a plan view of a control arm used in hydrostatic transmission.

FIG. 3 is a block diagram of one embodiment of the invention.

FIG. 4 is a block diagram of another embodiment of the invention.

FIG. 5 is a hydraulic schematic of an embodiment of this invention.

FIG. 6 is an electrical schematic of an embodiment of the invention.

FIG. 7 is an electrical schematic of another embodiment of theinvention.

FIG. 8 is an electrical schematic of yet another embodiment of theinvention.

FIG. 9 is a bottom view of a hydrostatic center section mounted in aportion of the transmission housing, showing portions of thetransmission in cross-section, and showing a bypass mechanism inaccordance with one embodiment of this invention, with the bypassmechanism in the “off” position.

FIG. 10 is a bottom view of the hydrostatic transmission shown in FIG.9, with the bypass mechanism in the “on” position.

FIG. 11 is an external side view of the center section of thehydrostatic transmission as shown in FIG. 9.

FIG. 12 is a cross-sectional side view of a center section of ahydrostatic transmission as shown in FIG. 10, with the bypass mechanismin the activated position.

FIG. 13A is a cross-sectional, partial side view of the check valvemounted in the center section of a hydrostatic transmission as shown inFIG. 9, incorporating a different embodiment of the invention, showingthe valve in the closed position.

FIG. 13B is a cross-sectional, partial side view of the check valve asshown in FIG. 13A, showing the valve in the open position.

FIG. 13C is a cross-sectional, partial side view of a check valve asshown in FIG. 13A, and also showing the valve in the closed position.

FIG. 14 is a bottom view of a center section of an HST encompassing oneembodiment of this invention.

FIG. 15 is a bottom view of a center section of an HST encompassinganother embodiment of this invention.

FIG. 16 is a cross-sectional partial view of an embodiment of thisinvention.

FIG. 17 is a cross-sectional partial view of an embodiment of thisinvention.

FIG. 18 is a cross-sectional partial view of an embodiment of thisinvention.

FIG. 19 is a schematic of a control lever shift pattern in accordancewith one embodiment of this invention.

FIG. 19A is a schematic of a control lever shift pattern in accordancewith one embodiment of this invention.

FIG. 20 is a partial cross-sectional view of an HST center sectionincorporating a rotary bypass actuator in accordance with one embodimentof this invention.

FIG. 21 is a bottom plan view of an integrated hydrostatic transmissionincorporating a foot pedal activation of one embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a view of a typical vehicle using a integrated hydrostatictransmission, namely tractor 10, showing various locations of controlmechanisms for mechanical bypass units. Different tractor manufacturershave different preferences for location of the mechanical bypassactuator, making it difficult for an IHT manufacturer to design a singleunit for all uses without expensive design modifications or use ofadditional linkages to accommodate such uses. For example, the bypass 12may be located on the panel immediately in front of the seat. Othermanufacturers prefer to have it mounted in location 12A at the rear ofthe tractor, while others require it to be located under the tractorseat at location 12B. Control lever 13 is generally used to controldirection and speed of the vehicle.

A typical control arm 14 is shown in FIG. 2, and is generally attachedto the external housing of the IHT unit. The tractor manufacturer willgenerally attach its own levers and linkages (not shown) to control arm14. The typical full range of control arm motion, and the typicalneutral band of a prior art HST (of approximately 1°) are shown in FIG.2. However, due to a lack of control by the IHT manufacturer, it ispossible that the tractor manufacturer's linkages may not properlydefine true neutral, due to manufacturing and design tolerances. Thus,when the user puts the tractor into what is believed to be “neutral,”there may be some creepage of the unit, requiring the user to hunt forthe actual “neutral” location. An IHT or HST in accordance with thepresent invention will have an expanded neutral band, as also shown inFIG. 2.

FIG. 3 is a block diagram of a standard hydrostatic unit showing pump 16and motor 18, which are connected through a hydraulic transfer system 20comprising, among other things, high pressure side 21 and low pressureside 22. These sides would reverse upon a change in direction of pump16. Input shaft 24 is driven by an external motive force (not shown) andacts to rotate pump cylinder block 34. This rotation causes axialmovement of pump pistons 25 mounted in pump cylinder block 34, causingthe pistons 25 to engage a thrust bearing in moveable swash plate 26.Hydraulic fluid is contained in hydraulic transfer system 20, and isforced via high pressure side 21 to motor 18, where the hydraulic fluidengages motor pistons 28, which are driven against fixed swash plate 32causing rotation of motor cylinder block 37 and driving output shaft 29.

Hydraulic circuit 20 also comprises sump 30, which can be an integralpart of the housing for the IHT. It is understood that sump 30 couldalso include elements of the transaxle such as a differential and othergearing and the output axles, engaged to the HST through output shaft29. Hydraulic oil is maintained in sump 30, and during operation of theunit is drawn through filter 35 towards check valves 31 and 33. Checkvalves are generally known in the art and are used to control flow intoor out of a controlled system, and valves 31 and 33 are shown in moredetail in other figures. Hydraulic transfer system 20 may compriseporting located in center section 39 on which pump 16 and motor 18 areboth rotatably mounted, or it could be integral with the casing for theHST or IHT. Other methods of hydraulically connecting the hydrostaticpump and motor are known in the art and are not intended to be excludedfrom this description.

In the embodiment shown in FIG. 3, check valve 31 is open as it isconnected to low pressure side 22 of the hydraulic circuit. Since checkvalve 33 is connected to high pressure side 21, the check ball of valve33 is seated, thus closing the valve. This design is generally used tobring fluid into the low pressure side to make up for fluid lost fromthe closed circuit due to, e.g., leakage. In one known prior art bypassdesign, motor cylinder block 37 is mechanically lifted off its runningsurface on center section 39 to allow fluid to exit the closed circuitquickly and return to sump 30.

Also shown in FIG. 3 is electromechanical bypass 40, which can betriggered by a signal generated in some manner to open check valves 31and 33 by pushing the check valves off the valve seats. Theelectromechanical bypass can be achieved in a variety of manners,including the use of solenoids, motors and so forth, which can be usedto accomplish the goal of opening and closing the system. For example,FIG. 4 shows a closed-loop hydraulic system similar in many respects tothe system shown in FIG. 3, with like numbers identifying like elements,and with the addition of a bypass shunt 44 and rotary bypass 46. Shunt44 must be located between the high and low pressure sides of thesystem. FIG. 4 also shows charge pump 36 and charge relief valve 52 usedto generate increased pressure in the porting system between sump 30 andcheck valves 31 or 33, and a cooling orifice 38. Charge pump 36 may bedriven off of input shaft 24 as is generally known in the art. It isunderstood that different types of electro-mechanical bypasses can beused in place of rotary bypass 46. In essence, any means of opening andclosing a shunt 44 between the high pressure side and the low pressureside which is triggered by an electrical signal could be used in thisinvention.

FIGS. 6–8 show electrical schematics of different embodiments of theinvention where like numerals indicate like elements. FIG. 6 shows asimple circuit with battery 50, ignition switch 51, bypass 40 and bypassactivation switch 54 mounted in series so that the bypass switch 54cannot be activated unless ignition 51 is on, for safety reasons, toprevent freewheeling when the vehicle is off and to eliminate thepossibility of a battery drain if the bypass switch is left on. In thealternative embodiment shown in FIG. 7, there is provided a secondbypass switch. The two switches could be activated in different manners;e.g., switch 54 could be mounted on the vehicle and second switch 56could be mounted with and controlled by the control lever 13 in a mannerto be described herein. FIG. 8 shows yet another embodiment, including atime out circuit 49 activated by switch 53, which may be mounted on thevehicle. Time out circuit 49, which can be of a type known in the art,may include a clock mechanism to open bypass 40 for a limited period oftime, and can include a separate switch to deactivate the bypass.

It will be understood from the prior discussion that this invention canbe incorporated into an HST or an IHT in a number of ways. For example,FIG. 9 is a cross-sectional plan view of the bottom of an HSTincorporating one embodiment of the present invention. Specifically,FIGS. 9–11 show a standard check valve mechanism, including check plugs(or valves) 61 mounted in center section 60; check balls 62 are held incheck plugs 61. Electro-mechanical bypass 40 comprises solenoid 41 andbypass plate 48. Solenoid 41 is a design known in the art and can besecured to center section 60 through a plurality of bolts 57 or otherstandard methods. It is connected to a switch, not shown in FIG. 9,through solenoid wire 58. Solenoid arm 42 has a spring 43 mountedthereon and is secured to bypass plate 48. Slots 64 are formed in bypassplate 48 to receive check balls 62.

FIG. 9 shows the unit in the “off” or non-bypass position. Screws 65 aremounted in bolt slots 67 in a manner to slidably secure bypass plate 48to center section 60. As will be understood, the term screw 65 should beread broadly to encompass a variety of methods of securing plate 48 tocenter section 60. When the solenoid is activated as shown in FIG. 10,plate 48 is pulled towards solenoid 41 by solenoid arm 42. As shown moreclearly in FIG. 12, plate 48 thus contacts check balls 62, pushing themoff their seat in center section 60 and placing the unit into bypass.Hydraulic fluid contained in chamber 52 internal to check plug 61 canthus exit the check valve 61 past check ball 62 through slot 64 inbypass plate 48. When solenoid 41 is switched to “off,” the plate 48 isreturned to its “off” position as shown in FIG. 9 via spring 43, thusreturning the check valves to their normal operation and restoring theclosed circuit. Thus, an HST in accordance with this invention canquickly go in and out of the bypass mode through simple activation of anelectronic circuit.

The embodiments shown herein use a standard check plug 61, which can bethreaded into center section 60 and include o-ring seals 45. The HSTshown in FIGS. 9 and 10 is of a standard design, incorporating motorcylinder block 37 and motor pistons 28 engaging fixed swash plate 32, abrake mechanism 47 is also shown and may be engaged to the motor outputshaft (not shown). It should be understood that this invention is notlimited to such embodiments, but could also be used with other checkvalve arrangements, including without limitation use of a separate checkplate to hold the check balls against the center section. In addition,any method of moving the plate 48 could be used in connection with thisinvention.

One element of this invention is the manner in which plate 48 is securedto center section 60. As shown in FIG. 12, a fixed height spacer 63 isused with screw 65 to maintain plate 48 the proper distance from centersection 60. FIGS. 13A to 13C show an alternative and preferred design ofthis connection means. Specifically, the fixed height spacer iseliminated and plate 48 is held against check plug 61 by screw 65 whichis engaged into center section 60. Spring 68 is secured to screw 65between the head thereof and plate 48 and acts to maintain plate 48 flatagainst the bottom surface of check plug 61. In the preferred embodimentthree screws 65, each with a spring 68, would be used. In FIG. 13A checkball 62 is in the normal closed position. In FIG. 13B, plate 48 has beenmoved to dislodge ball 62 and allow the flow of fluid out of chamber 52,achieving full bypass of the system. As can be seen, spring 68 isuncompressed in FIG. 13B. As fluid flow increases, the pressure on ball62 also increases, forcing plate 48 away from valve 61, thus allowingball 62 to reseat on internal seat 59, as shown in FIG. 13C, thusclosing the bypass.

Springs 68 also act to prevent excessive free-wheeling of the vehicle.If, for example, the vehicle is running downhill in the bypass mode,there would be no hydraulic braking to slow the vehicle, resulting in apotential safety hazard. In such a situation, hydraulic fluid would exitchamber 52 of the check valves, passing through slots 64 of bypass plate48 with increasing force. At some point, the force of hydraulic fluid onplate 48 as it is discharged from the hydraulic circuit, acting on thecheck ball 62, will overcome the compressive force of springs 68, andcheck ball 62 will act to lift plate 48 off check plug 61, allowingcheck ball 62 to reseat on internal seat 59, preventing uncontrolledfree wheeling through hydraulic braking. The spring constant K ofsprings 68 can be selected according to the desired point at which flowshould be slowed.

FIGS. 14 and 20 shows an alternative embodiment using a rotary bypassactuator 46 as shown in FIG. 4. Kidneys 70 a and 70 b are formed on pumprunning surface 72 of center section 60. Kidneys 70 a and 70 b form theaccess between the hydrostatic pump (not shown) and the internal portingcomprising the closed loop. A bore 74 can be drilled into center section60 and closed by cap 73, acting to connect the high pressure and lowpressure sides of the closed loop. Rotary actuator 46, which can be of astyle known in the art, includes arm 69 rotatably attached thereto. Arm69 may include passage 75 spaced to allow flow between the two sides ofthe closed loop. In FIG. 14, arm 69 is in the “on” or “bypass” mode,allowing a connection through passage 75, which can be sizedappropriately to control the amount of hydraulic fluid passingtherethrough, to prevent uncontrolled discharge. The sizes of thevarious ports required to prevent uncontrolled discharge will dependupon a variety of factors including, e.g., size of the vehicle, size ofthe transmission and the expected operating conditions. When rotaryactuator is switched “off,” as shown in FIG. 20, arm 69 rotates so thatpassage 75 is perpendicular to bore 74, thus restoring the closed loopsystem.

A further alternative embodiment is shown in FIG. 15, in which thebypass actuator is a plunge-type actuator 76 having arm 77 having afirst portion with a diameter sufficient to sufficiently block flow inbore 74 between the two sides of the closed loop, and a second portion78 having a smaller diameter, also sized to allow controlled dischargeof hydraulic fluid. When actuator 76 is switched “on,” arm 77 is pulledinwards so that arm portion 78 is located within bore 74 to allow flowbetween the two sides, effectively putting the unit in bypass mode.

FIG. 16 shows yet another alternative embodiment of the invention, andin particular a further means for displacing the check balls 62 fromseat 59 in check plugs 61. Cross plate 80 can be secured to the unit ina known manner to allow movement thereof towards check plugs 31.Projections 81 are formed on plate 80 and spaced to engage check balls62. When the electrical bypass circuit described herein is switched“on,” electromagnets 82 are energized and pull plate towards check plugs31 so that projections 81 knock the check balls 62 off seats 59,allowing the hydraulic fluid to exit chamber 52 so that the unit entersbypass mode. In such an embodiment, the force required to unseat balls62 could be fairly substantial and the current required forelectromagnet 82 could create undesirable heat in the unit. For such asituation, the unit could incorporate a two stage electrical circuitwith a high first current used to overcome the hydraulic resistance anddisplace balls 62 and a significantly lower second current used to holdplate 80 in place. When the bypass circuit is switched to the “off ”position, the plate will be forced back to its original position asshown in FIG. 16 by the force of gravity or through use of springs orother methods known in the art.

The embodiment shown herein discloses the check balls 62 being pushedoff seat 59 to achieve bypass. However, it is understood that bypasscould also be achieved by having the check balls 62 pulled off of seat59, as shown in FIG. 17, by for example an electromagnet 83 mountedinternal to said check plug 31 and specifically within chamber 52. Othermechanisms for such a purpose will be obvious to one skilled in the art.Yet another embodiment is shown in FIG. 18, where electromagnet 83 ismounted external to plug 31 and acts to pull member 84 towards it whenactivated to force ball 62 off seat 59 to achieve bypass.

The bypass system in accordance with the present invention is preferablyactivated by a switch engaged by control arm 13. A typical control armslot 86 is shown in FIG. 19, having forward, neutral and reversepositions. In accordance with the present invention, switch 88 islocated in the “neutral” area of the shift pattern, so that it can beoptionally activated by the user by moving control arm 13 to theappropriate location adjacent switch 88 to activate it. Switch 88 can beof a design known in the art, so that it is activated by contact witharm 13 or another member actuated by arm 13. By activating switch 88,the bypass feature is activated so that a true “neutral” position isachieved, i.e., the HST is effectively prevented from moving thetractor. This position, which activates switch 88, is effectively a“park” position, as the combination of arm 13 being in neutral and theunit entering full bypass effectively eliminates the possibility ofvehicle creepage.

As noted above, it is an object, of this invention to provide an HSTwith an improved wider neutral band, to overcome in part problems thatmay be created when the linkage of the tractor is connected to controlarm 14. An alternative embodiment shown in FIG. 19A shows a control armslot 86 with an enlarged neutral area. Plate 89 is operatively engagedto switch 88 to increase the size of the area where the above-described“park” feature of the HST can be engaged.

FIG. 21 represents yet another embodiment for engaging switch 88 toachieve bypass, through use of a standard foot pedal mechanism 91engaged to IHT 90 through standard linkage, such as wire rod 92, whichis formed with enlarged section 94 placed along the length of rod 92 soas to engage switch 88 when the foot pedal mechanism 91 is moved to theappropriate “neutral” position. Other alternative mechanisms foractivating the bypass could be used, and it is understood that thisinvention should not be so limited. By way of example only, a switchcould be located on the tractor on the main control panel or adjacentthe tractor seat.

It is to be understood that the above description of the inventionshould not be used to limit the invention, as other embodiments will beobvious to one skilled in the art. This invention should be read aslimited by the scope of its claims only.

1. A hydraulic apparatus comprising: a housing; a hydraulic mountingmember secured to the housing and comprising a pump running surface; ahydraulic pump located on the pump running surface; a hydraulic transfersystem at least partially formed in the hydraulic mounting member andconnected to the pump, the transfer system comprising a first side and asecond side; a bore formed in the hydraulic mounting member andconnecting the first side and the second side, wherein the bore extendsparallel to and below the pump running surface; and a valve in fluidcommunication with the hydraulic transfer system; an electrical actuatorcoupled to the valve; and wherein the electrically actuated valve has anopen position for fluidly connecting the first side and the second sideand a closed position for separating the first side and the second side.2. The hydraulic apparatus of in claim 1, wherein the valve movesrotationally.
 3. The hydraulic apparatus of claim 1, wherein the valvecomprises an arm that is moveable in a direction perpendicular to thebore.
 4. The hydraulic apparatus of claim 1, wherein the apparatus ismounted within a vehicle and the vehicle has a switch associated with aspeed control for controlling actuation of the valve.
 5. The hydraulicapparatus of claim 4, wherein the switch simultaneously actuates a timedelay circuit and the valve, and after a pre-established time expires,the time delay circuit causes the valve to assume the closed position.6. A hydraulic apparatus comprising: a housing; a sump formed within thehousing; a center section mounted within the housing, the center sectioncomprising porting; a hydraulic pump and a hydraulic motor mounted onthe center section; and a valve in fluid communication with the porting;and an electronic actuator mounted adjacent the center section andoperable to open and close the valve.
 7. The hydraulic apparatus ofclaim 6, wherein the porting comprises a first side and a second side,wherein a bore is positioned between and in fluid communication with thefirst side and second side and wherein the valve is mounted within thebore.
 8. The hydraulic apparatus of claim 7, wherein actuation of thevalve fluidly connects the first side and the second side.
 9. Thehydraulic apparatus of claim 8, wherein the apparatus is mounted withina vehicle and the vehicle includes a switch for actuating the valve. 10.The hydraulic apparatus of claim 9, wherein the switch is associatedwith a vehicle speed control.
 11. The hydraulic apparatus of claim 6,wherein actuation of the valve allows fluid communication between thesump and the hydraulic porting.
 12. The hydraulic apparatus of claim 11,wherein the apparatus is mounted within a vehicle and the vehicleincludes a switch for actuating the valve.
 13. The hydraulic apparatusof claim 12, wherein the switch is associated with a vehicle speedcontrol.
 14. A hydraulic apparatus comprising: a hydraulic pumprotatably mounted on a pump running surface; a hydraulic motor; arotating shaft driven by the motor; a hydraulic transfer systemcomprising a first hydraulic pressure side and a second hydraulicpressure side and connecting the hydraulic pump to the hydraulic motor,wherein during operation of the hydraulic pump, fluid is continuouslycirculated between the pump and the motor to cause rotation of theshaft; a valve positioned between the two hydraulic pressure sideswherein the valve is located directly below the pump running surface andthe valve extends in a direction parallel to the ump running surface;and an electrical mechanism positioned to actuate the valve; whereinactuation of the valve fluidly connects the first hydraulic pressureside and the second hydraulic pressure side.
 15. The hydraulic apparatusof claim 14, wherein the pump running surface is formed on a centersection and wherein at least a portion of the hydraulic transfer systemis located within the center section.
 16. The hydraulic apparatus ofclaim 15, wherein the valve is mounted to the center section and influid communication with the hydraulic transfer system.
 17. Thehydraulic apparatus of claim 16, wherein actuation of the valve by theelectrical mechanism allows fluid communication between the firsthydraulic pressure side and the second hydraulic pressure side.
 18. Thehydraulic apparatus of claim 14, wherein the motor is mounted on thecenter section.
 19. The hydraulic apparatus of claim 18, wherein thevalve is mounted to the center section and in fluid communication withthe hydraulic transfer system.
 20. The hydraulic apparatus of claim 14,wherein the apparatus is mounted within a vehicle and drivingly coupledto an axle of the vehicle.
 21. A hydraulic apparatus comprising: ahousing; a separate hydraulic mounting member secured to the housing; ahydraulic pump rotatably mounted on the hydraulic mounting member; ahydraulic transfer system connected to the pump, the hydraulic transfersystem comprising a first side and a second side; and an electricallyactuable arm extending into the separate hydraulic mounting member forfluidly connecting the first side and the second side.
 22. The hydraulicapparatus of claim 21, wherein actuation of the arm fluidly connects thefirst side and the second side.
 23. The hydraulic apparatus of claim 22,wherein the arm is actuated by being rotated.
 24. The hydraulicapparatus of claim 22, wherein the arm is actuated by being moved in alinear direction.
 25. The hydraulic apparatus of claim 21, wherein thehydraulic mounting member comprises a center section located within thehousing.
 26. A hydraulic apparatus comprising: a housing forming a sump;a hydraulic mounting member secured to the housing and located withinthe sump; a hydraulic pump mounted on the hydraulic mounting member; ahydraulic transfer system connected to the pump and the sump, thehydraulic transfer system comprising a first side and a second side; andan electrically movable arm extending into the hydraulic mounting memberfor fluidly connecting the first side and the second side.
 27. Thehydraulic apparatus of claim 26, wherein actuation of the arm fluidlyconnects the first side and the second side.
 28. The hydraulic apparatusof claim 27, wherein the arm is rotationally movable.
 29. The hydraulicapparatus of claim 27, wherein the arm is linearly movable.
 30. Thehydraulic apparatus of claim 26, wherein the hydraulic pump is mountedon a center section, which is located within the hydraulic apparatus.